<template>
  <div>
    <router-link v-show="showAbs" tag="div" to="/" class="header-abs">
      <div class="iconfont back-icon">&#xe624;</div>
    </router-link>
    <div class="header-fixed" v-show="!showAbs" :style="opacityStyle">
      <router-link to="/">
        <div class="iconfont header-fixed-back">&#xe624;</div>
      </router-link>
      景点详情
    </div>
  </div>
</template>

<script>

export default {
  name: 'DetailHeader',
  data () {
    return {
      showAbs: true,
      opacityStyle: {
        opacity: 0
      },
    }
  },
  methods: {
    handScroll () {
      let song = document.documentElement.scrollTop//获取滚动的值
      if(song > 50) {
        this.showAbs = false
        if(song < 140) {
          let opacity = song/140
          this.opacityStyle = {
             opacity 
            }
          }
        }
      else if(song < 50){
        this.showAbs = true
      }
    }
  },
  activated () {
    window.addEventListener('scroll',this.handScroll)//绑定一个监听事件监听滚动(scroll)
  },
  deactivated () {//这个生命周期函数是代表页面即将被隐藏或即将显示一个新的页面执行的函数
    window.removeEventListener('scroll',this.handScroll)//对全局事件进行解绑
  }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .header-abs
    position: absolute
    top: .2rem
    left: .2rem
    height: .8rem
    width: .8rem
    border-radius: .4rem
    background: rgba(0, 0, 0, .8)
    text-align: center
    line-height: .8rem
    .back-icon
      color: #fff 
      font-size: .4rem
  .header-fixed
    position: fixed
    top: 0
    right: 0
    left: 0
    height: $headerHeight
    line-height: $headerHeight
    text-align: center
    color: #fff
    background: $bgColor
    font-size: .32rem
    .header-fixed-back
      position: absolute
      top: 0
      left: 0
      width: .64rem
      text-align: center
      font-size: .4rem
      color: #fff 
</style>
